test: pin EvalCase session state injection into agent instructions

[sgoel2be24-cyber]

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Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: EvalCase session state data does not seem to be propagated #5037
• Related: EvalCase session state data does not seem to be propagated #5037

Problem:
Eval tools already saw EvalCase.session_input.state, but instruction templates with {some_key} historically did not during eval.

Solution:
Current main already runs inject_session_state for string instructions in the eval Runner. This PR adds a LocalEvalService regression so that path cannot silently break.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

1 passed — tests/unittests/evaluation/test_local_eval_service.py::test_eval_injects_session_input_state_into_instruction

Manual End-to-End (E2E) Tests:

Not applicable: this is a unit regression for eval instruction injection. No runtime/CLI surface change.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

Additional context

Assistance: drafted with an AI coding agent and reviewed before opening.

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